Wireless follies

The 2.4 GHz band provides a lot of fun. The antennas are easily available off the shelf, and can be attached to wide range of equipment, from those little analog video cameras to cordless phones to Bluetooth and WiFi equipment. They may range from a 7dBi omnidirectional whip through an arm-long 19dBi Yagi up to a 32dBi monstrosity welded from aluminium tubes. A lot of fun is possible when you don't care about the legal limits of EIRP.

A gain of a device can be also significantly increased by a parabolic reflector. 12-15 dB gain can be easily achieved just by putting an USB wifi dongle into a focal point of a suitably parabolic reflector; voila, WiFry, WokFi, or Woktenna. (Cf. cantenna made of a Pringles can; no gain to speak of but better directionality, therefore higher noise immunity.) Line-of-sight range of 3-5 km, and some of the parabolas come with a nice handle for handheld use.
http://www.usbwifi.orconhosting.net.nz/

A fun thing to do, when your window points in a suitable direction, is "wararmchairing". Put a high-gain antenna on the windowsill, sit in an armchair, and watch the data flowing in. Log the packets, grep the logfiles later, and you'll be surprised how many email passwords you will find there. And how many open file shares of Windows computers. And people's web-browsing habits. And often also something that looks like VoIP communication. All completely passive, without transmitting a single packet, with extremely low chance to be discovered. Often you get only one side of the communication, as to get both you'd have to see both the accesspoint and the client, but that may be enough for your purposes. A lot of data is in plaintext; also, there are attacks on WEP and WPA1 available now.

Web cafes and hotels are another interesting threat landscape. The networks there are often protected with a WEP key; however all the patrons/guests have the same key, and a passive packet monitor can then record the communication of all of them. I did a demo of this some time ago.

WiFi is not everything. Much fun can be had with Bluetooth. Some phones are vulnerable to bluesnarfing - the attacker can pilfer the data from the handheld device. As Bluetooth operates on 2.4 GHz as well, the same tricks for increasing range for WiFi - from woktennas to directly wiring a high-gain dish to the dongle - applies here as well.
http://en.wikipedia.org/wiki/Bluesnarfing

Do not underestimate the analog wireless cameras, often used as baby monitors. I wonder what could all be seen with a receiver with a high-gain antenna, from a hillside above a city or from a high-rise building. There was even a child abuse case here that was discovered due to somebody accidentally receiving signal from somebody else's baby monitor camera.
http://www.earthtimes.org/articles/show/172376.html

Denial-of-service attack on 2.4 GHz wireless is also rather easy to pull. If we'd want to "go nuclear", a microwave oven contains a magnetron tuned to the same frequency. 802.11n is however much more resistant against such jamming.
http://en.wikipedia.org/wiki/Electromagnetic_interference_at_2.4_GHz